The invention relates to a method for connecting the ends of steel tubes by means of orbital welding using hybrid technique as well as to a device for carrying out the method.
The invention relates in particular to tubes, preferably with wall thicknesses of more than 6 mm, in particular more than 12 mm, and diameters of preferably more than 150 mm, which tubes are connected to one another to form pipelines using different welding processes, such as for example laser beam welding and arc welding using hybrid technique. The term tubes as used hereinafter is to be understood as relating to round tubes as well as also to hollow tubes with varying cross sections.
Laser beam welding of tubes is generally known and efforts have continuously been undertaken to significantly reduce the seam cross section in comparison to the conventional arc welding processes, such as manual arc welding or metal inert gas welding (MIG), and to shorten welding times through higher welding speeds so as to improve efficiency.
DE 10 2008 029 724 A1 discloses a method for connecting thick-walled metal workpieces by means of welding, wherein three weld regions are provided in which welding involves a combination of welding processes, that is laser beam welding, hybrid laser arc welding, and arc welding.
U.S. Pat. No. 6,191,379 B1 describes processes which also combine welding processes, that is laser welding and TIG welding.
WO 2005/056230 A1 discloses for example as state of the art the combination of a metal inert gas welding method with a laser arc welding process, the so-called hybrid laser MIG welding, which is characterized in that the arc and the laser beam are arranged at a defined distance relative to one another and a higher gap bridging capability compared to a pure laser beam welding process can be attained.
With the device described there tubes are welded in mobile use by orbital welding technique to form pipelines.
In such a hybrid laser process, the laser beam and the arc of the MIG welding process impact simultaneously upon the weld site so that tube connections can be manufactured with high efficiency. The production of welded connections between the tubes is realized in this method by a welding device which revolves around the tube using orbital technique with a combined laser MIG welding head.
This method takes into account only to a limited extent the particular demands of hybrid welding such as, e.g., the adjustability of the arc root in relation to the laser beam axis, i.e. a change in distance between laser welding head and MIG welding head in circumferential direction is not possible at least not during the welding process.
Further disadvantageous are the comparably high weight of the combined hybrid welding head and moved masses as well as the limited flexibility with respect to process control, especially the geometry parameters of the hybrid welding head.
To suit the welding parameters to the respective welding position is particularly complicated when hybrid laser MIG welding is involved because the combination of two processes results in a high number of adjustment options. This is especially true for the geometric arrangements of laser beam and MIG welding torch, as shown in the WO 2005/056230 A1.
It is of particular drawback that the geometric parameters of the hybrid welding process can be adjusted during the process only in a very complicated way, when direct adaptation of a MIG torch to a laser beam processing optics is involved.
Orbital welding with a hybrid laser MIG welding process has the further drawback that the hybrid welding head known from the WO 2005/056230 A1 is composed of single components, respectively, which are not suited to one another to interact in an optimum way.
The solutions known to date for technical implementation of the hybrid laser MIG welding are therefore constructively complex, limited as far as adjustment options of the process parameters are concerned, and are characterized by a high weight.
In summary, it is noted that the state of the art at this time is absent of any industrially applicable orbital guidance system that is tuned to the demands of the hybrid laser arc welding in an optimum manner.
The known combined hybrid welding heads are appropriate for this application only to a limited extent because they have a comparably high weight, are inflexible during the welding process with respect to adjustability or setting capability of the geometric parameter, and as a result of their dimensions fail to meet the demands in particular for offshore welding.